PURPOSE: To enhance the bonding strength of a metal lead wire to an electrode in their bonding face by a method wherein 10 to 62% of 5 to 30μm pores in terms of the ratio of a surface area exist at least in a part where the metal lead wire is wire-bonded.

CONSTITUTION: A PZT element 10 is polished in parallel; the surface and the rear of the PZT element 10 are coated, by using a screen--printing operation, with a silver paste which contains about 2wt.% of bismuth oxide in a solid portion and whose average particle size is 0.3μm; the paste is dried and baked; intermediate layers 12 are formed coaxially. In addition, the intermediate layers 12 are coated with a silver paste by a screen-printing operation; the paste is dried and baked; electrode layers 14 are formed in such a way that their thickness is 10μm and that the ratio of pores to the area of the surface is about 10%. Metal lead wires are pressure-bonded to the electrode layers 14 and an ultrasonic vibration is applied. The metal lead wires are plastic-deformed in their bonding face, creep into the pores on the surface of the electrodes, bonded parts are formed, and the metal lead wires are brought into close contact with and bonded to the electrodes.